Previous to low-cost petroleum exploration, renewable energy sources were utilized. In fact, during the development of the compression ignition engine (U.S. Pat. No. 542,846 and U.S. Pat. No. 608,845) by Rudolph Diesel vegetable oils were utilized, according to the article by Shay, E. G. “Diesel fuel from vegetable oils: Status and opportunities.” Biomass and Bioenergy (1993) vol. 4 (4) pp. 227-242.
The concern for the greenhouse effect gases emission resulting from burning fossil fuels makes more relevant the utilization of sustainable sources. Biofuels derived from vegetable biomass, such as ethanol, are currently the only sustainable source of liquid fuel:
The most widely employed fuel is ethanol, which is the fermentation product of sucrose or glucose diluted solutions, according to the equation (1) below: (for glucose).C6H12O6→2CH3CH2OH+2CO2  (1)
However, for each 6 carbons present in the glucose molecule, only 4 will actually result in fuel. There is also the need for energy for ethanol distillation: even at optimized conditions, burning of most of the sugarcane bagasse is mandatory, see Ensinas, A. V. et al. Analysis of process steam demand reduction and electricity generation in sugar and ethanol production from sugarcane. Energy Conversion and Management (2007) vol. 48 (11) pp. 2978-2987.
Glucose can also be obtained from the acid or enzymatic hydrolysis of cellulose, according to the article by Huber, G. W. et al., Synthesis of transportation fuels from biomass: Chemistry, catalysts, and engineering. Chemical Reviews (2006) vol. 106 (9) pp. 4044-4098.
Cellulose, the main constituent of biomass, is the most common organic polymer. Its 1.5×1012 tons per year production makes it a practically inexhaustible raw material, see Klemm, D. et al., Cellulose: Fascinating Biopolymer and Sustainable Raw Material. Angewandte Chemie International Edition (2005) vol. 44 (22) pp. 3358-3393.
Other routes for converting biomass into fuels besides cellulose hydrolysis directed to ethanol production are known. Among those, fast pyrolysis for production of bio-oil and synthesis gas and the utilization of this latter for obtaining fuels. Gasification processes have the drawback of low thermal process efficiency (maximum 16 to 50% of the energy is recovered as fuel after synthesis), as cited by the Huber, G. W. et al, 2006 article.
On the other hand, the utilization of fast pyrolysis bio-oils as fuels is difficult, requiring further refining, still according the same article by Huber, G. W. et al., 2006.
Ethanol, successfully utilized in Otto cycle engines (gasoline), in view of its low cetane number cannot be used directly in Diesel cycle engines. However mixtures of petroleum-derived diesel fuel and ethanol can be successfully utilized provided additives for solubilizing such mixtures are used (surfactants and co-solvents). See in this respect the articles by Ribeiro, Núbia M. et al. “The role of additives for diesel and diesel blended (ethanol or biodiesel) fuels: A review.” Energy Fuels (2007) vol. 21 (4) pp. 2433 and Hansen, A. C. et al. “Ethanol-diesel fuel blends—A review.” Bioresource Technology (2005) vol. 96 (3) pp. 277-285. In practice, the utilization of ethanol is limited to 20 vol %.
Vegetable oil-derived compounds can be utilized in Diesel cycle engines, chiefly biodiesel, ethyl and methyl esters of fatty acids, see Ma, F. et al., Biodiesel production: A review. Bioresource Technology (1999) vol. 70 (1) pp. 1-15. However, the availability of vegetable oils is reduced when compared to that of cellulose.
Burning of oxygenated compounds-containing fuels such as ethanol, biodiesel and others in Diesel cycle engines has the advantage of reducing soot emission. See the articles by Curran, H. J. et al. “Detailed Chemical Kinetic Modeling of Diesel Combustion with Oxygenated Fuels.” Conference: 28th International Symposium on Combustion (2000); Westbrook, C. K. et al. “The effect of oxygenate molecular structure on soot production in direct-injection diesel engines.” SANDIA REPORT SAND2003-8207 (2003); and Pepiot-Desjardins, Perrine et al. “Structural group analysis for soot reduction tendency of oxygenated fuels.” Combustion and Flame (2008) vol. 154 (1-2) pp. 191-205.
A further important parameter in Diesel cycle engine fuels is the post compression ignition ability, expressed by the cetane number obtained in an engine, ASTM D613 Method, or in an equipment such as the IQT Ignition Quality Test, ASTM D6890, in this respect see Murphy, M. et al.—Compendium of Experimental Cetane Number Data. National Renewable Energy Laboratory (2004).
U.S. Pat. No. 2,575,543 reports the use of diethyl ether (DEE) which can be obtained from renewable sources (ethanol) in Diesel cycle engines, as start fuel. Mixtures from 15 to 50% by volume of DEE could be utilized in the fuel. The drawback of DEE is its low boiling point (34.6° C.) and specific weight (0.7134 g/cm3) in spite of the high cetane number (140-160, reported in the literature, see the above citation by Murphy, M. et al. (2004)).
U.S. Pat. No. 4,425,136 teaches the direct use of carbohydrates in furnaces, as solutions of water, ethanol and sucrose or any other soluble sugar. Water and ethanol are required respectively for solubilizing sugar and for starting the engine (volatile). C5 to C12 sugars are exemplified, including glucose. The drawback is that sugars tend to caramelize and form deposits in the engines, even at the more elevated combustion temperatures required for the invention (500° C.). This patent further teaches that the invention could be utilized in admixtures with diesel oil provided modifications in the engine are performed.
U.S. Pat. No. 4,891,049 teaches the use of carbonates as additives for Diesel cycle engine fuel. Fuels with up to 50 mass % carbonate are claimed, such as dimethyl carbonate (DMC).
In spite of the possibility of being obtained from regenerable sources, the cetane number of DMC is low, and its preferred use is as an additive in gasoline, see Pacheco, M. A. et al. Review of Dimethyl Carbonate (DMC) Manufacture and Its Characteristics as a Fuel Additive. Energy & Fuels (1997).
U.S. Pat. No. 5,308,365 relates to the utilization of diethers or triethers of glycerol as Diesel cycle engines additive in amounts up to 30 volume % in the fuel. It could be observed that the soot content was reduced. Glycerol can be considered as a renewable source, it being the by-product of the transesterification of fatty acids with alcohols (biodiesel production). However, as compared to the availability of other materials such as cellulose, the utilization potential of glycerol ethers as the fuel main constituent is reduced.
U.S. Pat. No. 6,015,440 teaches the use of glycerol ethers combined to biodiesel (fatty acid esters), resulting in lower cloud point in the biodiesel.
U.S. Pat. No. 5,820,640 describes the utilization of emulsions, mixtures of fast pyrolysis oil (bio-oil), up to 50% by weight, with diesel oil. The use of an emulsifier is required for solvency of the bio-oil into the diesel fuel. In spite of the production potential of huge amounts of bio-oil by fast pyrolysis, there are problems such as corrosion, ash content and sediments in the material. The use of the mixture in a diesel engine has not been evaluated in the patent.
U.S. Pat. No. 5,858,030 claims the use of dimethoxyalkanes such as dimethoxyethane (DMET) as additives for diesel oil. The cetane number of 1,2-dimethoxyethane is 105, and it can be produced in renewable form (oxidative coupling of the dimethyl ether, which can be obtained from synthesis gas) but has low flash point (0° C.).
U.S. Pat. No. 6,578,870 teaches the use of an oxygenated compound such as DMET to obtain a desired increase in the cetane number and a second oxygenate of higher flash point to obtain the desired flash point of the mixture.
U.S. Pat. Nos. 5,906,664 and 6,270,541 teach the use of dimethyl ether (DME) as fuel in Diesel cycle engines. Compositions of methyl alcohol, water and DME are claimed with a single-phase product with good ignition features. DME can be produced renewably (biomass, synthesis gas) but has the disadvantage of low flash point (−41° C.).
U.S. Pat. Nos. 6,872,231 and 7,300,476 teach the use of heavy oxygenates as Diesel additives, without the disadvantage of the low flash point. However those are obtained from the oxidation of fossil hydrocarbons.
U.S. Pat. Nos. 7,282,071 and 7,374,587 teach the use of hydrophobic starch as fuel, including diesel engines. Starch, in spite of being renewable, is obtained in lower profusion than cellulose, and is useful to other ends such as human food. Also, it is not completely dissolved in diesel fuel, which can impair combustion.
U.S. Pat. No. 7,014,668 teaches the use of a fuel for engines including those of the Diesel cycle, of a mixture of oxygenates from 5% to 100% by volume, and optionally hydrocarbons. The fuel of the invention has at least two distinct oxygenates, with a total of 4 functional groups in the mixture comprising the alcohol, ether, ester, ether nitrate, aldehyde, ketone, acetal, peroxide and epoxide. More preferably, the fuel would have at least one compound of each group described above.
U.S. Pat. No. 4,992,605 relates to the hydroconversion of vegetable oils on hydrotreating catalysts, leading to high cetane paraffin compounds corresponding to the fatty acids of the original triglycerides.
U.S. published Application 2006/0186020 teaches the hydroconversion of triglycerides in reactors for diesel HDT, admixed in the amount of up to 75 mass % of the feed, yielding the high cetane paraffin compounds already admixed to the diesel stream specified for use as fuel.
U.S. Pat. No. 7,279,018 relates to the hydrogenation of the same triglycerides, with further isomerization in order to reduce the cloud point of the product. The product from hydrogenation and isomerization is then admixed to diesel and optionally to another oxygenate. The drawback of these processes is that the availability of vegetable oils and animal fats (triglycerides) is not as high as that of cellulose.
U.S. published Application 2006/0096158 teaches the use of a cyclic ester or lactone for compounding gasoline or diesel fuel. The use as gasoline is preferred, since simple lactones, without long chains linked to the cycle, have high octane rate. A lactone such as γ-Valerolactone can be obtained from levulinic acid, which can be obtained from hydroxymethyl furfural, which in turn can be obtained from cellulose.
Other patents teach the production of non-oxygenated products from renewable sources such as terpenoids or isoprenoids (synthetic derivatives of isoprene).
U.S. Pat. No. 7,029,506 teaches the use of terpenes such as β-carotene and the like (carotenoids, carotene precursors) as additives for diesel fuel, in small amounts). The compounds can be extracted from plants such as broad beans (vicia faba) and certain seaweeds. The amount of carotene obtained from biomass is small.
U.S. published Application 2008/0083158 teaches the genetic modification of microorganisms for producing the farnesane isoprenoid and derivatives as well as the use of such compounds as additives for diesel fuel compounding. Farnesane is produced by cell cultivation, consuming sugars. Sugars are consumed by the development of biomass, generating the isoprenoid in small amount.
The multiplicity of patents directed to the preparation of renewable fuels for Diesel cycle engines demonstrates that the art still needs new products, of better ignition quality and obtained from biomass at a higher output. Broadly, the products have poor compatibility with petroleum-derived diesel fuel and are of low ignition ability (e.g. ethyl alcohol), or obtained from sources other than cellulose (e.g. biodiesel) or are obtained through extended series of operations which entail yield loss (e.g. products from synthesis gas, this latter being obtained from biomass gasification). The documents cited above relate to the use of renewable oxygenated compounds as main components of Diesel cycle engine fuels.
An additional possibility for use of renewable compounds is their application as ignition improvers. Usually nitrated compounds are utilized as cetane improvers, mainly 2-ethyl-hexyl-nitrate. Such compounds are usually derived of alcohols submitted to sulfonitric solutions (H2SO4+HNO3) or other nitration methods known in the art.
U.S. Pat. No. 2,066,506 teaches the use of nitrates of polyhydric alcohol derivatives, such as 1,2-propyleneglycol dinitrate. U.S. Pat. No. 2,378,466 teaches the use of the dinitrate of a poly(1,2-alkylene glycol) as cetane improver.
U.S. Pat. No. 2,280,217 teaches that light alkyl nitrates, such as ethyl nitrate (produced by the nitration of ethyl alcohol) can lead to flash point problems, heavy nitrates being preferred, with alkyl groups of more than 5, preferably more than 6, carbon atoms.
U.S. Pat. Nos. 4,405,335 and 4,406,665 relate respectively to the use of tetrahydrofurandiol dinitrate and of the tetrahydrofuranol nitrate as cetane improvers.
U.S. Pat. No. 4,659,335 teaches the use of nitric acid esters of monosaccharides and/or polysaccharides, preferably nitrocellulose, plus a polyether as cetane improvers.
U.S. Pat. No. 4,705,534 relates to the use of several polynitrates (polynitrates esters) plus selected amines (as stabilizers) for increased cetane in diesel and alcohol fuels. As polynitrates are cited ethylene glycol dinitrate, triethylene glycol dinitrate, nitroglycerin, cellulose tri-, di- and mononitrate and admixtures of same, among others. Nitrocellulose is sparingly soluble in hydrocarbons and its viscosity is high.
U.S. Pat. No. 5,096,462 relates to the use of nitric acid for dissolution of biomass cellulose, the resulting stream being then submitted to reaction with ethylene oxide (with alkylation of a few cellulose —OH groups, a reaction known as ethoxylation), and later the addition of a dehydrating agent such as H2SO4, plus HNO3, which eventually leads to nitration of the product. The nitrated product is then incorporated to an alcohol such as methanol or ethanol to be utilized in Diesel cycle engines. The utilization of this product as cetane additive in admixture with hydrocarbons is not claimed.
U.S. Pat. No. 5,454,842 deals with the use as cetane improver of the products of the nitration of fatty acids alcohols. Claimed contents for utilization in diesel fuel are from 0.01% to 2% by mass.
A further possibility of obtaining useful products straight from cellulose and/or sucrose involves the use of dianhydrohexitols. The dianhydrohexitols can be produced in the initial hydrolysis step, hexoses hydrogenation (glucose in case of cellulose or starch, and glucose plus fructose in case of sucrose) to hexitols (glucitol or sorbitol in case of D-glucose, and sorbitol plus mannitol in case of fructose) and further double dehydration, resulting in dianhydrohexitols (isosorbide or 1,4:3,6-Dianhydro-D-glucitol in case of sorbitol and isomannide or 1,4:3,6-Dianhydro-D-mannitol from mannitol), of formula C6H10O4.
Dianhydrohexitols are represented by the general structure (describing isosorbide, isomannide and isoidide isomers) illustrated by Formula 1 below.

The preparation of dianhydrohexitols by conversion of cellulose biomass can be advantageous if compared to the preparation of ethanol, since all the carbons present in cellulose (and sucrose) are converted into the end product. Further, separation schemes not involving distillation can be employed with significant energetic efficiency. A selective process for obtaining isosorbide from cellulose using hydrated molten salts is known. In this respect see the article by Almeida, R. M. et al., Lignocellulosics Conversion in a Molten Salt Hydrate Medium into Platform Chemical/Fuel—Conference Catalysis for Ultra Clean Fuels—Dalian, China, 21-24 Julho 2008.
Dianhydrohexitols such as isosorbide have been utilized as PVC plasticizer and renewable monomer. Derivatives such as isosorbide mononitrate and dinitrate are used in the treatment of myocardial infarction. See in this respect the article by Flèche, G.; Huchette, M., Isosorbide—preparation, properties and chemistry. Starch/Stärke, vol. 38, n 1, (1986), S 0.26-30.
Most of the processes for hexitols dehydration are not selective. The acidic medium process of sorbitol (glucitol) dehydration leads to the initial formation of 1,4 and 2,5 anhydro-D-glucitol—both compounds being known as sorbitan. In the sequence, 1,4 anhydro-D-glucitol can be dehydrated into 1,4-3,6 dianhydro-D-glucitol (isosorbide). 2,5 anhydro-D-glucitol on its turn does not undergo the second dehydration.
The mixture containing preferably the products of the first sorbitol dehydration is called sorbitan and is easily esterified with fatty acids. U.S. Pat. No. 4,297,290 describes a process for obtaining sorbitan esters. Sorbitan esters, used as surfactants, are commercially available from several manufacturers: see Ullmann's Encyclopaedia of Industrial Chemistry 2002, Wiley-Surfactants/Nonionic Surfactants. DOI: 10.1002/14356007.a25-747.
According to the teachings of U.S. Pat. No. 4,477,258, sorbitan esters are utilized in formulations of diesel fuel-containing emulsions. Contents from 97 to 90% by volume of diesel fuel are admixed to an aqueous solution of ethanol and/or methanol of at least 5% of the total, and from 3 to 10% by volume of an emulsifying mixture containing sorbitan monooleate and an ethoxylated non-ionic surfactant.
U.S. Pat. No. 4,604,102 cites the utilization of an additive pack for Diesel cycle engines containing (i) a combustion accelerator (organic nitrate) and (ii) sorbitan esters, reducing coking in the fuel injection nozzles. Preferably the amount of the mixture of (i) and (ii) in the fuel is from 0.01 to 1% by mass.
U.S. Pat. No. 6,156,081 teaches the formulation of a further additive pack for corrosion inhibition and ease of combustion, containing a surfactant agent—a sorbitan ester, lubricant oil and a saturated hydrocarbon containing from 14 to 17 carbons is claimed. The claimed ratio of diesel fuel for the additive pack is from 1:200 to 1:2,000.
U.S. Pat. No. 6,527,816 teaches the utilization of isosorbide-derived compounds as detergents for lowering deposits in gasoline. The compounds are obtained from the reaction of isosorbide with epoxide-containing groups. Reported contents in the Examples are of 400 mg of the compound/L gasoline.
U.S. Pat. No. 6,648,929 and U.S. Pat. No. 6,858,046 (continuation) teach water-emulsified fuel compositions containing sorbitan esters as one of the components of the claimed additive pack.
U.S. Pat. No. 7,182,797 teaches the utilization of a pack of additives for diesel fuel containing sorbitan oleate, a polyoxyethylene alcohol, an alkylene glycol and an amine.
An alkyl ether of isosorbide, dimethyl isosorbide, is utilized as component of personal care products and in drug formulations, see the article by Malhotra, S. V. et al. Applications of Corn-Based Chemistry. The Bridge (2007) vol. 37 (4).
Processes for the production of dimethyl isosorbide are known in the art, such as in International Application WO 2007/096511, where isosorbide is treated with methyl chloride in the presence of an alkaline agent.
U.S. Pat. No. 4,585,649 teaches dentifrice formulations (which include tooth paste, mouth wash, chewing gum, tooth sticks and dental floss) containing monoethers and diethers of dianhydrohexitols. The monoethers and diethers of isosorbide were effective to reduce the multiplication of plaque-causing bacteria.
The state-of-the-art illustrates the multiplicity of solutions presented for obtaining renewable fuels for Diesel cycle engines. However a fuel other than ethanol derived from cellulose is still sought, said fuel showing solubility in diesel, combustion ability (high cetane), which could be obtained in high yields and utilized in significant amounts in petroleum derived diesel fuel.
Thus, there is still the need in the technique of compositions for use in Diesel cycle engines based on dianhydrohexitols having the desired features of high specific mass, flash point, oxygen content, boiling point and combustion ability which enable their use. Still, as a particular case, the use of dianhydrohexitols dinitrates is claimed in the present application as combustion accelerators.
Also needed in the technique, oxygenates from renewable sources which can be utilized as components of a Diesel cycle engine, in any amount, such compounds being described and claimed in the present application.